Costimulation blockade in rheumatic diseases: where we are?

Study of the association between CD28/CTLA-4 expression and disease activity in juvenile idiopathic arthritis

The aim of the present study was to investigate the immune function of children with juvenile idiopathic arthritis (JIA). Flow cytometry and three-color direct immunofluorescence were used to examine cluster of differentiation (CD)3⁺ T-lymphocyte subsets and CD28/cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) expression in whole blood (using the no-wash method) from 36 children with JIA and 39 healthy children. During the active phase of JIA, CD28 expression on CD4⁺ T cells in children with JIA was significantly reduced; thus, CD4⁺CD28^- T-cell frequency increased, suggesting that CD4⁺ T-cell and CD4⁺CD28^- T-cell apoptosis was inhibited in patients with JIA. The continued survival of these immune-active T lymphocytes may promote the occurrence and development of JIA. CTLA-4 expression levels on CD4⁺ and CD8⁺ T cells in children with JIA during the active phase were significantly higher than those in normal controls. As the majority of CD4⁺ T cells in patients with JIA are CD28^-, they cannot be inactivated by the interaction between CTLA-4 and B7, leading to continuously high levels of CTLA-4 expression on the surface of CD4⁺ T cells without functional effect. Hence, T lymphocytes are continuously kept in a highly activated state that is difficult to stop. During the resting phase, the CD4⁺ and CD8⁺ T-cell counts in children with JIA were similar to normal, and CD28 expression was also normal. This suggests that the frequency of CD4⁺CD28^- T cells can be used as an indicator of the active phase of JIA. CTLA-4 expression on the surface of T cells in children with JIA during the resting phase was also similar to that in normal controls, suggesting that abnormal lymphocyte activation plays an important role in the active phase of JIA.

Bone remodelling markers in rheumatoid arthritis

Bone loss in rheumatoid arthritis (RA) patients results from chronic inflammation and can lead to osteoporosis and fractures. A few bone remodeling markers have been studied in RA witnessing bone formation (osteocalcin), serum aminoterminal propeptide of type I collagen (PINP), serum carboxyterminal propeptide of type I collagen (ICTP), bone alkaline phosphatase (BAP), osteocalcin (OC), and bone resorption: C-terminal telopeptide of type 1 collagen (I-CTX), N-terminal telopeptide of type 1 collagen (I-NTX), pyridinolines (DPD and PYD), and tartrate-resistant acid phosphatase (TRAP). Bone resorption can be seen either in periarticular bone (demineralization and erosion) or in the total skeleton (osteoporosis). Whatever the location, bone resorption results from activation of osteoclasts when the ratio between osteoprotegerin and receptor activator of nuclear factor kappa-B ligand (OPG/RANKL) is decreased under influence of various proinflammatory cytokines. Bone remodeling markers also allow physicians to evaluate the effect of drugs used in RA like biologic agents, which reduce inflammation and exert a protecting effect on bone. We will discuss in this review changes in bone markers remodeling in patients with RA treated with biologics.

Immunosuppression by co-stimulatory molecules: inhibition of CD2-CD48/CD58 interaction by peptides from CD2 to suppress progression of collagen-induced arthritis in mice

Targeting co-stimulatory molecules to modulate the immune response has been shown to have useful therapeutic effects for autoimmune diseases. Among the co-stimulatory molecules, CD2 and CD58 are very important in the early stages of generation of an immune response. Our goal was to utilize CD2-derived peptides to modulate protein-protein interactions between CD2 and CD58, thereby modulating the immune response. Several peptides were designed based on the structure of the CD58-binding domain of CD2 protein. Among the CD2-derived peptides, peptide 6 from the F and C β-strand region of CD2 protein exhibited inhibition of cell-cell adhesion in the nanomolar concentration range. Peptide 6 was evaluated for its ability to bind to CD58 in Caco-2 cells and to CD48 in T cells from rodents. A molecular model was proposed for binding a peptide to CD58 and CD48 using docking studies. Furthermore, in vivo studies were carried out to evaluate the therapeutic ability of the peptide to modulate the immune response in the collagen-induced arthritis (CIA) mouse model. In vivo studies indicated that peptide 6 was able to suppress the progression of CIA. Evaluation of the antigenicity of peptides in CIA and transgenic animal models indicated that this peptide is not immunogenic.

The expression and anatomical distribution of BTLA and its ligand HVEM in rheumatoid synovium

Co-inhibitory signaling from B and T lymphocyte attenuator (BTLA) can suppress lymphocyte activation and maintain peripheral tolerance. However, the expression and anatomical distribution of BTLA and its ligand, herpesvirus entry mediator (HVEM), in rheumatoid arthritis (RA) synovium have not been reported. In this study, we analyzed the expression of HVEM and BTLA in RA synovium by immunohistochemistry, and our results showed that both factors were observed in all four cases of RA samples. At the cellular level, both HVEM and BTLA were found on the cell membrane and in the cytoplasm. Fluorescence dual staining demonstrated that HVEM was chiefly on CD3(+) T cells, CD68(+) macrophages, and to a lesser extent was found on CD31(+) endothelial cells. Similarly, the expression of BTLA was observed on infiltrated CD3(+) T cells and CD68(+) macrophages. The co-expression of HVEM and BTLA with some members of the B7 family in these sections was also analyzed, and the results showed that HVEM antigen was also found on B7-H3(+) capillaries, while it was absent on B7-H1(+), B7-DC(+), B7-H4(+), and Z39Ig(+) cells. Interestingly, BTLA was observed on B7-H1(+), B7-H4(+), and HVEM(+) cells in the synovium. The characteristic expression and distribution of BTLA/HVEM in the synovium indicated that their signaling probably affects the pathogenesis of RA, and a clear understanding of their functional roles may further elucidate the pathogenesis of this disease.

The expression and distribution of immunomodulatory proteins B7-H1, B7-DC, B7-H3, and B7-H4 in rheumatoid synovium

CD28/B7 signals have been shown to have the capacity to regulate T cell activation and participate in regulating the development of rheumatoid arthritis (RA). However, the expression and anatomical distribution of some members of the B7 superfamily including B7-H1, B7-DC, B7-H3 and B7-H4 in RA synovium is still unclear. We analyzed the expression of these molecules in synovial tissues from RA patients. Immunohistochemistry showed that all of these molecules were observed in synovium. On the cellular level, all of them were found on cell membrane and in cytoplasma. The expression of B7-DC and B7-H3 was major on capillaries, synovicytes and infiltrated inflammatory cells in the lining layer, while B7-H1 and B7-H4 were detected in some inflammatory cells residing in the sublining and lining layer. Fluorescent dual staining indicated that all these molecules were principally associated with CD31(+) endothelial cells and CD68(+) macrophages. In addition, B7-H1 and B7-H3 were also observed on CD3(+) T cells (including CD4(+) and CD8(+) T cells). Interestingly, B7-H1/B7-H4, B7-H3/B7-DC were co-expressed on the same cells. The characteristic expression and distribution of these molecules in synovium indicated that they probably have different effects during the progress of RA, and a clear understanding of their functional roles may further elucidate the pathogenesis of this disease.

Abatacept in the treatment of polyarticular JIA: development, clinical utility, and place in therapy

Juvenile idiopathic arthritis (JIA) is a group of chronic arthritides affecting children. The polyarthritis category, affecting five or more joints in the first six months, tends to be more aggressive, leading to a destructive joint disease with significant morbidity, disability, and costs to society. The current treatment regimen, which primarily combines methotrexate and tumor necrosis factor alpha (TNF-α) blockade, still leaves a significant group of patients with an inadequate response. Therefore, the development of new medications that act via other mechanisms of pathogenesis is necessary. T cell lymphocytes are key components in the immune reaction in JIA. Cytotoxic lymphocyte-associated antigen-4 (CTLA-4) is a potent inhibitor of the costimulation pathway necessary to activate T cells. Abatacept is a recombinant fusion protein comprising the extracellular part of human CTLA-4 connected to a modified Fc part of IgG-1. In a randomized, multinational, blinded withdrawal study in children with polyarticular JIA, abatacept was found to be effective in about 70% of the patients, including 39% of TNF-α blockade failures, with significantly fewer flares occurring during the withdrawal phase than in patients receiving placebo. Abatacept continued to show good efficacy in a three-year open-label extension study, with a beneficial effect on health-related quality of life. The safety profile of abatacept is generally good. In 2008, the US Food and Drug Administration approved abatacept for use in children over six years of age with JIA and a polyarticular course. In 2010, the European Medicines Agency gave approval for abatacept to be used in combination with methotrexate for those who fail at least one disease-modifying medication and TNF-α blockade.

Pharmacogenetics of rheumatoid arthritis: Potential targets from susceptibility genes and present therapies

Rheumatoid arthritis (RA) is a chronic heterogeneous autoimmune disorder of unknown etiology resulting in inflammation in the synovium, cartilage, and bone. Genetic factors play an important role in susceptibility to RA as the heritability of RA is between 50% and 60%, with the human leukocyte antigen (HLA) locus accounting for at least 30% of overall genetic risk. Outside the major histocompatibility complex (MHC) region, six additional risk loci have been identified and validated including PTPN22, STAT4, PADI4, CTLA4, TNFAIP3-OLIG3, and TRAF1/C5. Genetic factors are also important in RA pharmacotherapy due to the gene-dependent activity of enzymes involved in the pharmacokinetics and/or pharmacodynamics of RA medications. Indeed, there is great variability in drug efficacy as well as adverse events associated with any anti-rheumatic therapy and genetics is thought to contribute significantly to this inter-individual variability in response. This review will summarize the genetic factors that have been implicated in the pathogenesis of RA, and how these determinants may factor into the potential pharmacogenetics of this disease. We will also review the therapeutic agents that are currently being utilized or presently being evaluated in the treatment of RA, along with potential pharmacogenetic markers that have been proposed for such medications.

The discovery of novel experimental therapies for inflammatory arthritis

Conventional and biologic disease-modifying antirheumatic drugs have revolutionized the medical therapy of inflammatory arthritis. However, it remains unclear as to what can be done to treat immune-mediated chronic inflammation after patients become refractory to these therapies or develop serious side-effects and/or infections forcing drug withdrawal. Because of these concerns it is imperative that novel targets be continuously identified and experimental strategies designed to test potential arthritis interventions in vitro, but more importantly, in well-validated animal models of inflammatory arthritis. Over the past few years, sphingosine-1-phosphate, interleukin-7 receptor, spleen tyrosine kinase, extracellular signal-regulated kinase, mitogen-activated protein kinase 5/p38 kinase regulated/activated protein kinase, micro-RNAs, tumor necrosis factor-related apoptosis inducing ligand and the polyubiquitin-proteasome pathway were identified as promising novel targets for potential antiarthritis drug development. Indeed several experimental compounds alter the biological activity of these targets and have shown clinical efficacy in animal models of arthritis. A few of them have even entered the first phase of human clinical trials.

Costimulation of Th17 cells: Adding fuel or putting out the fire in the inflamed gut?

Inflammatory bowel disease, typified by Crohn's disease and ulcerative colitis, is a common disorder characterized by recurrent and serious inflammation of the gastrointestinal tract. It is well documented that T cells play a pivotal role in the development of inflammatory bowel disease. Th17 cells are a unique T cell subpopulation implicated in inflammatory bowel disease and many other autoimmune/inflammatory diseases. However, the regulatory mechanism of Th17 activation and proliferation has not been defined completely. Recent studies have shown that the ligation of several costimulatory receptor-ligand pairs contributes to the activation, differentiation, and proliferation of T lymphocytes including the Th17 subset. In this review, we will discuss the emerging evidence on the role of Th17 cells in inflammatory bowel disease pathogenesis as well as the effect of costimulatory molecules on Th17 development and consider if the need for such costimulation of T lymphocytes provides a target for the development of novel therapeutic strategy.

Development and validation of gene therapies in autoimmune diseases: Epidemiology to animal models

Recent advancement in immunology, molecular biology, and bioinformatics has yielded extensive information on the pathophysiological mechanisms of autoimmunity, which has greatly facilitated the identification of potential therapeutic targets and the development of gene therapy in the treatment of autoimmune disease. Preclinical studies were carried out in animal models. This phenomenon is well illustrated in two prototypic animal models of autoimmune disease: the autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS) and collagen-induced arthritis (CIA) model in rheumatoid arthritis (RA). Here we discuss the current data on the development and validation of gene therapy in autoimmunity in these two models. The success in preclinical animal model studies provides the proof-of-concept of gene therapy for potential future applications in the treatment of autoimmune diseases. Furthermore, the identification of risk factors from epidemiological studies reveals further potential therapeutic targets to be examined in animal models.